Since the late 1900s, semiconductor memories have been used in a variety of electronic devices including PCs and demand therefor has rapidly increased. With such market demand, the degree of integration of semiconductor devices has been increased year by year based on the development of semiconductor processing technology.
For high integration of semiconductor devices, although much research has been carried out to reduce device size, downscaling of the devices has reached a physical limit. Recently, studies are being actively carried out to improve the integration degree by changing conditions other than device size. Particularly, there have proposed a method of stacking memory cells formed of a stackable material one above another and a method of improving information storage capacity of a device to store multiple pieces of information in one cell (multi-level cell technology).
For ReRAMs, research is being conducted to realize a highly integrated memory using 3D stacking technology, taking advantage of the fact that all processes can be performed at a lower temperature than silicon processes and the thin film forming process is simple. However, a switching mechanism causing ReRAM behavior has not yet been clarified and several research groups are continuing to study the principles of resistance change. In addition, in order to put ReRAMs into practical use, it is essential to develop new materials and optimal deposition process technology and to secure device stability and uniformity.